It is recognized that susceptibility to infections increases with age. Moreover, infections in older individuals are associated with high morbidity and mortality. Herpes zoster (HZ) is a common affliction of the elderly, thought to be due to reactivation of the latent varicella zoster virus (VZV). It is of interest that reactivation of other herpesviruses, herpes simplex (HSV) and cytomegalovirus (CMV), does not appear to be more common in the elderly. The mechanisms responsible for the increased frequency of HZ are not known. Current thinking is that this is not due to suppression of humoral immunity, but may be due to imparment of certain factors involved in cell mediated immune (CMI) response. It will be the purpose of this project to assess whether certain immune defects due to the aging process are operative, or whether the increased incidence of HZ in the elderly is due to the unique nature of VZV infection itself. The approach will involve comparison in elderly and younger subjects of certain in vitro parameters of CMI response to VZV, HSV and CMV antigens, and T-cell mitogens. Specific methods will include analysis for antigen reactive cells, first generation lymphocyte response, and production of lymphokine including immune interferon. The project may help elucidate mechanisms of resistance to viruses, and may suggest means of prevention or amelioration of HZ in the elderly.